Insert ring for pistons



United States Patent INSERT RING FOR PISTONS Everett G. Fahlman, Medina,Ohio, assignor to The gilrmold Company, Medina, Ohio, a corporation ofApplication February 17, 1954, Serial No. 410,789

3 Claims. (Cl. 309-14) This invention relates to aluminum alloy pistonsin which a cast iron reinforcing band is provided in the head of thepiston that is grooved to receive the uppermost plston rmg.

In high speed, heavy duty, internal combustion engines the heads of thepistons are subjected to intense heat which softens the metal of analuminum alloy piston to an extent such that the steel piston ring inthe upper groove of the piston head tends to gradually widen its grooveby a hammering action on the side walls of the groove, thereby reducingthe effectiveness of the seal and shortening the life of the piston. Toeliminate this difiiculty, aluminum alloy pistons have sometimes beenprovided with a carrier band of iron embedded in the piston head andgrooved to receive a piston ring. Such carrier bands being of greaterstrength and being more heat resistant that the aluminum of the pistonbody, are able to withstand the hammering action of the piston ring, butthere are certain difficulties incident to the manufacture and use ofsuch carrier bands. The casting of the piston with the iron bandembedded in the body of the piston presents certain difliculties and thefact that the ferrous alloy of the carrier band is a poorer conductor ofheat than the aluminum piston body, tends to impede the transfer of heatfrom the piston head to the cylinder wall and increase the temperatureto which the piston head is heated in service.

When a carrier ring is employed which has a coefficient of expansionmaterially different from that of the aluminum alloy forming the body ofthe piston, severe stresses tending to distort the piston and thecarrier band and to weaken the bond between the band and the piston bodyare set up in the piston in the process of casting the same, with theresult that subsequent heating and cooling of the piston causesdeterioration of the bond. Iron alloys having a relatively highcoefficient of expansion and having the requisite strength of heatresisting bodies when cast are commercially available and it is possibleto obtain such an iron alloy that has a coefficient of expansionsubstantially the same as that of the high silicon aluminum alloyscommonly used in making cast aluminum pistons. The use of cast ironbands of such iron alloys eliminates the difficulties due to unequalrates of expansion, but the problem of permanently fixing the embeddediron carrier band to the aluminum body of the piston and the problem ofminimizing the heat blocking effect of the iron carrier band stillremains.

The iron carrier band can be firmly anchored in the piston head and agood heat conducting connection between the piston body and the carrierring can be obtained by providing an integral aluminum iron alloy bondbetween the aluminum of the piston and the embedded carrier band. Such abond has heretofore been provided by first suspending the carrier bandin molten aluminum for a length of time sufiicient to enable thealuminum to alloy itself to the band by'means of a thin layer ofaluminum iron alloy and then casting the piston about the band while thealuminum coating is still in a fluid state. This method, however, addsvery materially to the cost of manufacturing a piston.

The present invention provides a piston in which a mechanical bond ofadequate strength is provided between the piston ring carrier band andthe metal of the piston head and in which superior heat conduction isprovided from the face portion of the head through the carrier band tothe piston ring.

In addition, the present invention provides a construc- 2,707,136Patented Apr. 26, 1955 tion which closely spaced inspection openings areprovided 1n the carrier ring throughout its circumference and in WhlChthe ring is so constructed that it is not materially weakened by theopenings. Portions of the carrier ring that are enveloped by thealuminum of the piston are so formed that a relatively large surfacearea of the carrier band contacts with portions of the piston that areheated in service to the highest temperatures so as to provide for amore rapid transfer of heat from the aluminum piston body to the carrierring. The carrier ring is also formed with anchoring projections andrecesses that are so shaped that they offer a minimum resistance to flowof the aluminum alloy in the mold during solidification so that closecontact of the aluminum with the carrier band is obtained and initialstresses in the cast aluminum piston body due to the presence of theiron ring are reduced to a minimum.

The carrier band of the present invention is formed of an austeniticcast iron containing a relatively high percentage of nickel. Thecoefficient of expansion of such alloys can be varied by increasing ordecreasing the nickel content and may be made to correspond very closelyto the coefficient of expansion of the particular aluminum alloy used inthe piston. These iron nickel alloys also have good heat resistantproperties, dovnot grow appreciably after repeated heating and cooling,and are resistant to oxidation even at the casting temperature ofaluminum. An example of an iron alloy having the properties abovereferred to is an alloy containing 14% to 20% of nickel, about 5% ofcopper and 1% to 4% of chromium.

Objects of the present invention are to provide an aluminum alloy pistonhaving an iron piston ring carrier band that is joined to the metal ofthe piston by a firm mechanical bond which resists relativecircumferential, axial and radial movements of the band with respect tothe piston body, to provide a piston in which the band is so formed thatthe molten aluminum alloy can flow freely past and around the band andthe mold and remain in close contact therewith throughout the surfacesof the band that are embedded in the piston after the casting is cooled,to provide a piston in which the band is so formed that it has a largesurface area contacting with the metal of the piston head on the sidethereof facing the piston head face, and to provide effective conductionof heat from the piston head to the band.

A further object of the invention is to provide the piston ring carrierband with a large number of inspection openings at the bottom of thepiston ring receiving groove and to so dispose said openings withrespect to the anchoring ribs that the ring is not materially weakenedby the openings.

Reference should be had to the accompanying drawings forming a part ofthis specification, in which:

Figure 1 is a perspective view of a carrier band in the form which ithas prior to being placed in the piston mold;

Fig. 2 is a central vertical section of a piston in which a piston ringcarrier band has been embedded and showing (tihe piston ring receivinggroove cut in the iron carrier Fig. 3 is a fragmentary horizontalsection taken on the line indicated at 3--3 in Fig. 2; and

Fig. 4 is a fragmentary vertical section through the piston wall on anenlarged scale.

In the accompanying drawings the head. portion of an aluminum alloypiston 10 is shown, the piston having a top face 11 that is subjected toheated gases in the combustion chamber of an engine and an iron pistoncarrier band 12 that is embedded in the head portion of the pistonadjacent the face 11. The ring 12 is accurately po sitioned in thepiston mold by clamping the peripheral portion thereof between the copeand the drag of the mold. After the piston is cast the periphery of thecasting is machined to true cylindrical form so that the periphery ofthe ring 12 is flush with the periphery of the piston body. The "ring 12is provided with an annular row of regularly spaced projections 13 thatare spaced uniformly from the exterior periphery of the band. Each ofthe projections 13 is circumferentially elongated and has alongitudinally arcuate top edge 14 that merges at its ends into the topface of the ring 12.

Inwardly of each of the projections 13 and centrally disposed withrespect thereto a notch 15 is formed in the ring 12. Each notch 15 isnarrower than. the projection within which it is positioned, the widthof each notch being preferably less than half the length of theprojection. The bottom wall 16 of each notch is flush with the face ofthe adjacent projection 13 and the lower end wall 17 of each notch isabove the bottom face of the band and preferably near the median planeof the band, The band 12 has top and bottom faces 18 and 19 that tapertoward the outer periphery of the band. The outer portions of thesefaces are preferably machined to provide an accurate fit with ledges onthe cope and drag which position the ring in the mold. The top andbottom corners 20 and 21 of the ring at the interior periphery of thering are rounded to lessen resistance to the flow of molten metal in themold and to avoid the creation of internal stresses in the casting incooling. The projections 13 have transversely rounded longitudinal edges22 and the notches 15 have rounded edges 23 that permit the molten metalto flow more freely around the projections and into the notches duringcasting and to maintain close contact with the surfaces of the bondduring solidification so that internal stresses due to thesolidification of the aluminum around the iron band are minimized.

A piston ring groove 24 is cut in the band 12 after the piston has beencast and this groove is preferably of a depth to intersect the notches15 and to form an opening 25 to each of the notches which will permitvisual inspection of the bond between the aluminum and the iron band atclosely spaced points throughout the circumference of the band.

The projections 13 and the entire interior of the carrier band haverough surfaces that are formed in casting the band and these surfacesstrengthen the mechanical bond between the aluminum of the piston bodyand the carrier band. By providing the projections 13 and the notches 15opening to the top face of the carrier band, a large area of contact isprovided between the carrier band and the portion of the piston headabove the carrier band and, since the top portion of the piston head isheated to a higher temperature than other portions of the piston, thelarger area of contact with the more highly heated portions of thepiston offsets to a great extent the heat blocking effect of the carrierdue to its lower heat conductivity.

It is to be understood that in accordance with the pro visions of thepatent statutes, variations and modifications of the specific devicesherein shown and described may be made without departing from the spiritof the invention.

What I claim is:

1. A cast aluminum alloy piston having a cast metal reinforcing bandembedded in the head portion thereof, said band being composed of aferrous alloy having a coeflicient of expansion approximately the sameas that of the aluminum alloy of the piston and being positioned in saidhead with its exterior periphery at the piston periphery and with theremainder thereof enveloped by the metal of the piston, said band havingan annular row of circumferentially elongated projections on its topface that are in a zone intermediate the interior and exterior marginsof said top face and spaced inwardly from the piston periphery, saidprojections being spaced circumferentially and having longitudinal edgesof arcuate form, said band having a notch extending downwardly from itstop face inwardly of each of said projections and terminating above thebottom face of said band, said band being embedded in the piston withsaid projections extending toward the piston head face and with themetal of the piston filling said notches, said piston having acircumferential piston ring receiving groove cut in said band to a depthto extend into said notches and into the metal of the piston body insaid notches, said groove forming spaced openings in said band that arebridged by said projections.

2. A cast aluminum alloy piston having a cast metal reinforcing bandembedded in the head portion thereof, said band being composed of aferrous alloy having a coefficient of expansion approximately the sameas that of the aluminum alloy of the piston and being positioned in saidhead with its exterior periphery at the piston periphery and with theremainder thereof enveloped by the metal of the piston, said band havingan annular row of circumferentially elongated projections on its topface that are in a zone intermediate the interior and exterior marginsof said top face and spaced inwardly from the piston periphery, saidprojections being spaced circumferentially and having longitudinal edgesof arcuate form, said band having a notch extending downwardly from itstop face inwardly of each of said projections and terminating above thebottom face of said band, said band being embedded in the piston withsaid projections extending toward the piston head face and with themetal of the piston filling said notches, the notched interior of saidring and said projections having rough surfaces, the edges of saidnotches being rounded and the arcuate edges of said projections beingtransversely rounded, said piston having a piston ring receiving groovecut in said band to a depth to intersect said notches.

3. A cast aluminum alloy piston having a cast metal reinforcing bandembedded in the head portion thereof, said band being composed of aferrous alloy having a coefficient of expansion approximately the sameas that of the aluminum alloy of the piston and being positioned in saidhead with its exterior periphery at the piston periphery and with theremainder thereof enveloped by the metal of the piston, said band havingan annular row of circumferentially elongated projections on its topface that are in a zone intermediate the interior and exterior marginsof said top face and spaced inwardly from the piston periphery, saidprojections having longitudinal edges of arcuate form that merge intosaid top face at. their ends, said projections being of uniform size andregularly spaced, said band having a notch extending downwardly from itstop face inwardly of each projection and terminating above the bottomface of the band, each notch being disposed centrally of a projectionwith its bottom flush with an inner face of the projection, said bandbeing embedded in the piston with said projections extending toward thepiston head face and with the metal of the piston filling said notches,said piston having a circumferential piston ring receiving groove cut insaid band to a depth to intersect said notches and extend into the metalof the piston body in said notches, said groove providing spacedinspection openings in said band that are bridged by said projections.

References Cited in the file of this patent UNITED STATES PATENTS1,979,335 Mahle Nov. 6, 1934 2,124,360 Welty July 19, 1938 2,255,006Graham Sept. 2, 1941 OTHER REFERENCES Automotive Industries, Vol. 105,Issue No. 9, Nov. 1, 1951. Inside of back cover.

